1. Field of the Invention
The present invention relates to a flame-retardant resin having excellent moldability. More particularly, it relates to such a flame-retardant resin composed essentially of a specific fluorine-containing copolymer obtained by the copolymerizatin of tetrafluoroethylene, chlorotrifluoroethylene and ethylene.
2. Description of the Background
In recent years, attention has been drawn to flame-retardant resins having a high oxygen index, low fuming property and low dripping property as coating materials for plenum cables or as fire proofing materials. As one of the resins having such properties, a fluorine-containing copolymer of chlorotrifluoroethylene (hereinafter referred to simply as CTFE) with ethylene (hereinafter referred to simply as ET) is known. For example, some CTFE/ET type copolymers are disclosed in U.S. Pat. Nos. 3,847,881 and 3,767,634, West German Patent Publication No. 2,613,691 and Japanese Examined Patent Publication No. 32786/1974.
However, conventional CTFE/ET type copolymers usually have a relatively low thermal decomposition temperature at a level of about 320.degree. C. Fluorine-containing copolymers having a relatively high thermal decomposition temperature, tend to have a high melting point at a level of at least 250.degree. C. In any case, they have a drawback that the moldable temperature range is narrow. The above-mentioned publications also disclose copolymers of tetrafluoroethylene (hereinafter referred to simply as TFE) with ET and CTFE/TFE/ET type copolymers. However, these copolymers have drawbacks such that the oxygen index is small, or dripping takes place at the time of combustion, thus the flame retardancy is not necessarily satisfactory.